Zouma, 19, was part of the France team that won the Under-20 World Cup last year and moves for a reported fee of around 12.5 million pounds.

A statement on the Chelsea website read: "Chelsea Football Club has today (Friday) signed Kurt Zouma from St. Etienne. He will remain on loan at the French club for the rest of the season. The 19-year-old central defender has joined Chelsea on a five-and-a-half year contract. This season he has made 12 league appearances for France's fourth-placed side.

"The 6ft 2in Zouma is a French Under-21 international. He was born in Lyon and joined St. Etienne as a 15-year-old in 2009, turning professional in 2011. In total he has made 52 league appearances for 'Les Verts' and scored four goals. We will be monitoring his progress for the rest of the season here on chelseafc.com."

Zouma, who has attracted the attention of many clubs across Europe this season, was banned for 10 matches in November for a leg-breaking tackle on Sochaux midfielder Thomas Guerbert. He hinted earlier this month that he would like to move to Chelsea, suggesting he had already spoken with Mourinho.